This is a proposal to study some of the biological, biochemical, and biophysical characteristics of respiratory syncytial virus. Specifically, we shall determine such parameters as the kinetics of virion and messenger RNA synthesis in vivo. Molecular probes will be developed for some of this work. A detailed analysis of the viral polypeptide composition is planned as is an attempt to relate the different messenger RNAs to the polypeptides they code for. An attempt will be made to map the genome of the virus by U.V. irradiation of the infected cell. Finally, as temperature-sensitive mutants of the virus become available to us, these will be used to further characterize intracellular events in the virus' replication.